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flow rules: openflow rules that are configured on an openvswitch

Conceptual model 

This section will describe conceptually how distributed routing and network ACL's are achieved in an example VPC deployment with three tiers with VM's spanning three hosts. Further sections builds on the concepts/design principles introduced in this section to elaborate the architecture and design on how CloudStack and OVS plug-in can orchestrate setting up VPC's with distributed routing and network ACL's. 

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